Method and apparatus for chilling mold elements

ABSTRACT

This disclosure relates to a method and apparatus for continuously chilling or cooling mold parts which are subjected to heated products, such as the die elements of a plastic blow molding apparatus. More particularly, the disclosed method and apparatus is adapted to maintain a predetermined mold chilling temperature to permit rapid forming of plastic articles and reduce the dwell time of the plastic article within the mold. The disclosed apparatus includes a heat exchanger-evaporator, a first liquid coolant loop communicating with the heat exchanger and the mold parts to be cooled, wherein low viscosity liquid coolant is pumped through the heat exchanger and the mold parts to chill the mold parts, and a second coolant loop communicating with the evaporator within the heat exchanger and including a compressor, condenser and expansion valve. The coolant in the second coolant loop is evaporated by the expansion valve, within the evaporator of the heat exchanger, to absorb heat from and chill the coolant within the first coolant loop.

Unite States atent 1 Heider et a1.

[ METHOD AND APPARATUS FOR CHILLING MOLD ELEMENTS [75] Inventors: James Elmer Heider, Toledo;

Thomas H. Schult, Perrysburg, both of Ohio [73] Assignee: Owens-Illinois, Inc., Toledo, Ohio [22] Filed: Apr. 23, 1971 [21] Appl. No.: 136,861

1 July 31, 1973 Primary Examiner-Meyer Perlin Assistant Examiner-Ronald C. Capossela Att0rneyPhilip M. Rice and E. J. Holler [57] ABSTRACT This disclosure relates to a method and apparatus for continuously chilling or cooling mold parts which are subjected to heated products, such as the die elements of a plastic blow molding apparatus. More particularly, the disclosed method and apparatus is adapted to maintain a predetermined mold chilling temperature to permit rapid forming of plastic articles and reduce the dwell time of the plastic article within the mold. The disclosed apparatus includes a heat exchangerevaporator, a first liquid coolant loop communicating with the heat exchanger and the mold parts to be cooled, wherein low viscosity liquid coolant is pumped through the heat exchanger and the mold parts to chill the mold parts, and a second coolant loop communicating with the evaporator within the heat exchanger and including a compressor, condenser and expansion valve. The coolant in the second coolant loop is evaporated by the expansion valve, within the evaporator of the heat exchanger, to absorb heat from and chill the coolant within the first coolant loop.

2 Claims, 1 Drawing Figure PATENIED JUL3 1 3. 748 866 INVEN'I'OR.

JAMES E. HEIDER. BY OMAS H. SCHULT METHOD AND APPARATUS FOR CHILLING MOLD ELEMENTS BACKGROUND OF THE INVENTION This invention relates generally to refrigeration systems, including the process of chilling mold parts and a chilling or refrigeration apparatus.

One method of chilling the die elements of a mold is described in United States Letters Patent No. 3,127,753. The method described in this patent involves evaporation or boiling a refrigerant in mold cooling passages provided in the die elements. The refrigerant gas is then circulated to a condenser and compressor wherein the gas is condensed to a liquid and returned to the die elements. One of the major problems with the method described in the above referenced patent is the difficulty of maintaining balanced cooling between the die elements, because the refrigerant or coolant is evaporated within the die elements. Unless complicated flow control systems are utilized, the die elements cool unevenly. This problem is multiplied where several molds are utilized. There is also a problem with leaks and contamination, which is very serious in an evaporative cooling system because the refrigerant compressor is directly affected, resulting in poor compressor performance and rapid compressor wear.

One solution to the problems inherent in a vaporliquid phase refrigerant system would be to utilize a low temperature liquid coolant, in that the heat transfer characteristics of a liquid coolant would be more uniform and leakage would be more easily controlled. The major problem with a liquid coolant system is however, that most liquids utilized as coolants become very viscous at low temperatures and have poor heat transfer characteristics at low temperatures. The prevailing plastics industry view on liquid coolants for example is that, on temperatures below about 30 Fahrenheit, the pumping costs become prohibitive because of the increasing viscosity of the liquid. The method and apparatus of this invention utilizes a two refrigerant loop system, wherein a low viscosity liquid coolant is pumped through the die element of the mold to be chilled, which has been cooled in a heat exchanger which forms the common link between the loops. The second loop is preferably a vapor-liquid refrigeration system, wherein the coolant is vaporized within the common heat exchanger.

The method and apparatus of this invention is capable of maintaining stable temperature operations in a plastic blow-molding apparatus, for example, producing 5,000 plastic bottles per hour from two pair of cooperating die elements. The lower the temperature of the die elements of a mold, the faster the plastic in contact with the die faces will cool, permitting greater production rates. In fact, a plot of the cooling time versus temperature indicates that the time of cooling increases exponentially with the temperature of the die face. Lowering of the mold temperature from 40 Fahrenheit to -40 Fahrenheit, for example, cuts the cooling time by about 30 percent, permitting a corresponding increase in the production rate.

The method of chilling the die elements of this invention, includes circulating a low viscosity, low temperature fluid coolant under pressure through the molds at a temperature low enough to maintain stable operation, circulating the low viscosity fluid from the molds to a heat exchanger, wherein the temperature of the fluid coolant is reduced by a second coolant, evaporating the second coolant within the heat exchanger to transfer the heat absorbed by the low viscosity coolant to the second coolant, and circulating the second coolant to a condenser wherein the coolant is condensed, cooled and recirculated to the heat exchanger for evaporation. The apparatus of this invention includes a heat exchanger having an evaporator, a first coolant loop communicating with the heat exchanger and the die elements of the mold, and a pump adapted to circulate a liquid coolant under pressure through the heat exchanger and the die elements. A second coolant loop is provided which communicates with the evaporator of the heat exchanger, a condenser adapted to condense the coolant within the second coolant loop and an expansion valve adapted to vaporized the coolant within the second coolant loop, within the evaporator. The low viscosity coolant within the first coolant loop is preferably circulated in the liquid state under pressure from the heat exchanger, through the die elements of the mold, and the heat absorbed thereby is transferred to the coolant in the second coolant loop.

It can be seen from the above, that the method and apparatus of this invention combines the advantages of the liquid and the liquid-vapor coolant systems and avoids many of the problems of each system. The method and apparatus of this invention is also capable of maintaining a stable temperature in the die elements of a molding apparatus and avoids the problem of uneven cooling inherent in the liquid-vapor refrigeration systems.

The method and apparatus of this invention may thus be utilized to cool or chill a plurality of die elements in a high production molding apparatus. Other advantages and meritorious features of this invention will more fully appear from the following description of the preferred embodiment, claims and accompanying drawing, wherein:

The FIGURE is a schematic illustration of one embodiment of the apparatus for chilling mold elements of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The method and apparatus of this invention is adapted to chill the die elements of a molding apparatus, such as shown at 20 in the FIGURE. As described above, the refrigeration or cooling system of this invention is particularly adapted to chilling a mold apparatus having a high production rate, wherein the temperature of the coolant must be maintained at a relatively low temperature to maintain the stability of the system. The mold apparatus disclosed in the FIGURE is a conventional plastic blow molding apparatus, which might be utilized for example in the production of plastic bottles.

The mold halves 22 and 24 each receive and retain a die element 26 and 28, respectively. The die elements are urged together and apart by a pair of piston elements or rams 30 and 32. It will be understood however, that the method and apparatus of this invention is suitable for chilling various types of mold apparatus and is not limited to the particular blow molding apparatus disclosed.

The apparatus of this invention includes a first coolant loop 34 which is adapted to pump a low viscosity coolant, at a low temperature, through the mold apparatus 20 to cool the die elements 26 and 28. The first ratus through line 40 and mold coolant inlet lines 42. The die elements 26 and 28 may be provided with coolant channels as disclosed in the above referenced patent, or a plurality of baffles may be provided on the rearward surface of the die element, opposite the mating surfaces, to provide the requisite heat transfer characteristics. The coolant leaves the mold apparatus through outlets 44. In this embodiment, a pair of flexible bellows-like sections 46 are provided to permit opening and closing of the mold sections 22 and 24. The coolant is then returned to the pump 54 through lines 48, 50 and 52, where the coolant is recycled to the heat exchanger 36. The pump may be a conventional commercially available liquid centrifugal pump,or the like. A reserve tank 56 is provided in this embodiment to replenish any losses of the coolant in the system, through line 58, and drain line 64 is provided to permit emptying of the system. The drain line may be provided with a manual valve 62 and a reservoir 66.

i A suitable low viscosity coolant for the first loop of the chilling apparatus disclosed in the FIGURE is Refrigerant 11', which is a standard of the American Society of Heating, Refrigerating and Air Conditioning Engineers (Standard 34-66). The chemical formulation for Refrigerant 1 1 is CCl F which is sold by the Du Pont de Nemours Corporation under the trade name of Freon. As described above, the coolant utilized in the first coolant loop is preferably a low viscosity coolant, which is capable of being pumped through the system at the low temperatures required. Further, in the preferred embodiment of the invention, the coolant is pumped through the first coolant loop 34 in the liquid state, and therefore the temperature must be maintained below the vaporization temperature of the coolant, at the pressure maintained in the fluid lines. A low viscosity coolant may be characterized as a liquid coolant having a viscosity near one centipoise at the temperature of operation. Refrigerant 11, for example, has a viscosity of 0.9 centipoise at minus 40 Fahrenheit. It will be understood however, that any coolant which has the desired characteristics may be utilized in the chilling apparatus of this invention.

The second coolant loop 68 of the mold chilling apparatus of this invention is adapted to lower the temperature of the coolant in the first coolant loop 34, as described above. The coolant vapor from the evaporator coil 38 is utilized in the suction line heat exchanger 70 to cool the liquid coolant received through line 1 18, as will be described hereinbelow. The coolant vapor is received in the suction line heat exchanger through line 72. The suction line heat exchanger 70 communicates with a filter 74 through line 76. The filter 74 may be a conventional coolant vapor filter, and is adapted to filter out foreign material from the vapor including dirt and other debris from the heat exchangers 36 and 70. The filter communicates with the two-stage compressor 78 through line 80. The two-stage compressor illustrated in the FIGURE is a conventional refrigeration compressor, which is adapted to increase the pressure of the coolant vapor sufficiently to permit condensing of the vapor at a later stage. The compressor includes a first stage 82 which communicates with the second stage 84 through line 86. A common drive shaft 88 is provided between the compressor units. An oil separator 90 is provided in the second loop to remove anyoil received through line 92 from the second stage of the compressor 84. In this embodiment, a conventional.

high pressure control 94 is provided, which is merely a shut off valve to stop the operation of the compressor in the event the pressure in the system increased beyond a predetermined limit. An oil return line 96 is provided between the oil separator and the second stage 84 of the compressor. It will be understood that the oil separator 90 may be any conventional type of oil separator.

A condenser 98 communicates with the oil separator 90 through line 100, wherein the coolant vapor is condensed to a liquid. The temperature of the liquid cool ant leaving the condenser is generally between and Fahrenheit. The increase in temperature is of course caused by the increase in pressure. The fluid coolant is then received in a subcooler 102, through line 106. The subcooler may be a conventional shelltube heat exchanger having an evaporator 104 therein. A portion of the fluid coolant in this embodiment is channeled through line 108 and vaporized by the thermostatic expansion valve 110 in the evaporator 104. A valve 112 controls the volume of fluid channeled through line 108 to maintain the desired temperature of the fluid coolant leaving the subcooler through line 118. A suitable valve would be a conventional solenoid on-off valve, which is manually controlled to maintain the temperature of the liquid coolant within the predetermined temperature limits. Alternatively, an automatic solenoid valve may be provided having a thermocouple control, which controls the flow of liquid coolant through line 108 to maintain the predetermined temperature of the coolant leaving the subcooler 102. Line 114 communicates with the evaporator 104 in the subcooler and returns the coolant vapor to the first stage of the compressor 82.

The liquid coolant in line 118 is further cooled by the suction line heat exchanger 70, wherein the vapor received from the heat exchanger 36 at between minus 50 and minus 60 Fahrenheit is received in heat exchange relation with the liquid coolant. The suction line heat exchanger 70 may also be a conventional shell-tube heat exchanger, as described above. Finally, the liquid coolant, whose temperature is now about 0 Fahrenheit, is vaporized in the heat exchanger evaporator coil 38 by the thermostatic expansion valve 120, through line 124. A valve 122 is provided to control the rate of flow of the liquid coolant to maintain a predetermined temperature of the liquid coolant in the first coolant loop, as described above. The thermostatic expansion valves 120 and 110 may be conventional refrigeration system expansion valves which are commercially available. The valve 122 may be a manually operated solenoid valve similar to the valve 112 described hereinabove, or an automatic solenoid valve may be utilized.

A suitable coolant for the second loop 68 of the mold chilling apparatus of this invention is Refrigerant 502, which is also standard of the American Society of Heating, Refrigerating and Air Conditioning Engineers and is commercially available from Du Pont de Nemours Corporation under the trade name Freon. The individual elements of the mold chilling apparatus of this invention, including the compressor, heat exchangers, valves, condenser, oil separator, filter, pump and the like, have not been described herein in detail because each of these elements are well known in the art and are commercially available. Reference may also be made to the above referenced patent. Further, no claim is made herein to the specific details of the construction of these elements.

The method of continuously chilling the die elements 26 and 28 should be obvious from the above description of the mold chilling apparatus. Briefly, it includes circulating a low viscosity fluid coolant, such as Refrigerant 11, under pressure through the molds 22 and 24 at a temperature low enough to maintain the chilling temperature of the molds. In the disclosed embodiments of the apparatus, the temperature of the fluid coolant may be between minus 40 and minus 60 Fahrenheit, however, it will be understood that the preferred temperature will depend upon the type of molding apparatus and the rate of production. The liquid coolant in the first coolant loop 34 is then circulated to the heat exchanger 36, wherein the temperature of the fluid coolant is reduced by the coolant in the second coolant loop 68. The coolant in the second coolant loop is evaporated in the evaporator coil 38 in the heat exchanger 36, transferring the heat absorbed by the low viscosity fluid coolant in the first coolant loop to the coolant in the second coolant loop. Finally, the coolant vapor in the second coolant loop is circulated to the compressor 78 and the condenser 98 wherein it is condensed, cooled and recirculated to the heat exchanger 36. In the disclosed embodiment, the liquid coolant in the second coolant loop is also cooled in stages by the subcooler 102 and the suction line heat exchanger 70.

It will be understood that the method of continuously cooling or chilling the die elements 26 and 28 of this invention does not require a particular liquid-vapor refrigeration system, such as shown by the second loop 68 of the FIGURE. This embodiment is shown to illustrate a refrigeration system which is capable of cooling the liquid coolant in the first coolant loop 34 to a temperature low enough to maintain the temperature stability of the disclosed mold apparatus. Therefore, other suitable refrigeration systems may also be used depending upon the temperature requirements of the system.

We claim:

1. In a continuous plastic molding apparatus having opposed, relatively movable die elements receiving molten plastic material for forming plastic articles, the improvement comprising: a heat exchanger having an evaporator therein, a first continuous coolant loop having trichlorofluoromethane coolant therein communicating with said heat exchanger and the surfaces of said die elements opposite the die forming faces which are cyclicly heated to a high temperature over short time intervals, and a second coolant loop having a relatively volatile coolant therein communicating with said heat exchanger, a condenser adapted to condense the volatile coolant within said second coolant loop and an expansion valve means adapted to vaporize the volatile coolant within said evaporator, whereby the coolant within said first coolant loop is circulated and remains in the liquid state under pressure from said heat exchanger to repeatedly chill said die elements, and the heat of said molten plastic material is first absorbed by the trichlorofluoromethane coolant circulated in said first coolant loop and is later absorbed by the second relatively volatile coolant within said heat exchanger.

2. A method of continuously chilling opposed, relatively movable die elements of a continuous plastic molding apparatus, said die elements being repeatedly heated to high temperatures over short time intervals by receiving molten plastic material for forming plastic articles, comprising the steps of:

a. circulating trichlorofluoromethane liquid coolant, under pressure, into heat transfer contact with the surfaces of said die elements, opposite the die forming faces,

b. circulating said trichlorofluoromethane coolant from said mold parts to a heat exchanger, wherein the temperature of the liquid coolant is reduced by a relatively volatile coolant, thereby maintaining the trichlorofluoromethane coolant in a liquid state,

. evaporating said relatively volatile coolant within said heat exchanger, transferring the heat absorbed by said trichlorofluoromethane coolant from said surfaces of said die elements to said relatively volatile coolant, vaporizing said relatively volatile coolant, and

d. circulating said relatively volatile coolant vapor to a condenser, wherein said volatile coolant is condensed, cooled and recirculated to said heat exchanger. 

1. In a continuous plastic molding apparatus having opposed, relatively movable die elements receiving molten plastic material for forming plastic articles, the improvement comprising: a heat exchanger having an evaporator therein, a first continuous coolant loop having trichlorofluoromethane coolant therein communicating with said heat exchanger and the surfaces of said die elements opposite the die forming faces which are cyclicly heated to a high temperature over short time intervals, and a second coolant loop having a relatively volatile coolant therein communicating with said heat exchanger, a condenser adapted to condense the volatile coolant within said second coolant loop and an expansion valve means adapted to vaporize the volatile coolant within said evaporator, whereby the coolant within said first coolant loop is circulated and remains in the liquid state under pressure from said heat exchanger to repeatedly chill said die elements, and the heat of said molten plastic material is first absorbed by the trichlorofluoromethane coolant circulated in said first coolant loop and is later absorbed by the second relatively volatile coolant within said heat exchanger.
 2. A method of continuously chilling opposed, relatively movable die elements of a continuous plastic molding apparatus, said die elements being repeatedly heated to high temperatures over short time intervals by receiving molten plastic material for forming plastic articles, comprising the steps of: a. circulating trichlorofluoromethane liquid coolant, under pressure, into heat transfer contact with the surfaces of said die elements, opposite the die forming faces, b. circulating said trichlorofluoromethane coolant from said mold parts to a heat exchanger, wherein the temperature of the liquid coolant is reduced by a relativEly volatile coolant, thereby maintaining the trichlorofluoromethane coolant in a liquid state, c. evaporating said relatively volatile coolant within said heat exchanger, transferring the heat absorbed by said trichlorofluoromethane coolant from said surfaces of said die elements to said relatively volatile coolant, vaporizing said relatively volatile coolant, and d. circulating said relatively volatile coolant vapor to a condenser, wherein said volatile coolant is condensed, cooled and recirculated to said heat exchanger. 